Too much mulch will kill a tree

Thursday

Sep 27, 2012 at 12:01 AMSep 27, 2012 at 6:57 AM

Landscapers do good work on lawns. However, they kill trees by using too much mulch around the base of trunks. The International Society of Arboriculture says that "North American landscapes are falling victim to a plague of over-mulching." You see it everywhere: trees sitting in tidy mounds of mulch, dying.

Will Barbeau

Landscapers do good work on lawns. However, they kill trees by using too much mulch around the base of trunks. The International Society of Arboriculture says that "North American landscapes are falling victim to a plague of over-mulching." You see it everywhere: trees sitting in tidy mounds of mulch, dying.

The society says 2 to 4 inches of mulch in a cone is "over-mulching." It publishes a pamphlet with drawings illustrating proper mulching, urging property owners to "tell your landscaper."

It's astounding that landscaping "professionals" don't know these facts. Are they blinded by the point that mulching earns them extra income?

I was clueless until I noticed three trees planted by the Town of Barrington, R.I., 30 years ago. My neighbor has two of them; I have the other. They are the same species, planted the same day. They grew up looking alike through the decades. When a new neighbor bought the house next door a few years ago, he also brought in a landscaper who piled mounds of mulch around the tree trunks. My tree now looks flush with health while its two sisters next door are stunted and losing leaves too soon. Barrington's town arborist explained why.

A circle of mulch around the base of a tree is OK, if it's kept away from the trunk. Two to 4 inches of depth is OK, but keep it flat so water will not run off. The mistake landscapers make is to build a small "volcano"-shaped mound around the base of the tree trunk. According to the society's pamphlet:
-- Continuous moisture around the trunk base causes cankers and splits and lets disease and pests attack.
-- Excess moisture in the root zone stresses the plant and causes root rot.
-- Thick blankets of mulch become matted and prevent water and air from getting to the roots.

The society recommends:

Keep mulch flat, not mounded, so that water will not run off. Apply a 2- to 4-inch layer. Do not mulch near the trunk. If mulch is piled against the trunk or stem, pull it back several inches so that the base of the trunk and stem crown are exposed.

The town arborist thinks that my neighbor's trees can recover in four or five years after the mulch is removed. For more detailed information, look up "mulch volcanoes" through the Google search engine. Or consult the book "How Trees Die," by Jeff Gillman.

Will Barbeau lives in Barrington, R.I.

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